Some internal combustion engines (hereinafter also referred to as engines) for vehicles have a supercharger (hereinafter also referred to as a turbocharger), which utilizes the energy of exhaust gas. The turbocharger typically includes a turbine wheel which is rotated by the flow of exhaust gas through the engine's exhaust gas path, a compressor impeller which forcedly introduces air in an intake air path into the engine's combustion chamber, and a shaft which connects the turbine wheel and the compressor impeller. In the turbocharger having such a structure, the turbine wheel located in the exhaust gas path is rotated by the energy of exhaust gas, whereby the compressor impeller located in the intake air path is rotated to compress the intake air, which is then forcedly introduced into the combustion chamber of each cylinder.
A variable nozzle vane turbocharger, which can adjust boost pressure caused by the energy of exhaust gas, is becoming a mainstream in-vehicle turbocharger.
The variable nozzle vane turbocharger includes, for example, a variable nozzle vane mechanism (VN mechanism) provided in an exhaust gas flow path in a turbine housing and having a plurality of nozzle vanes (also called as movable vanes) which can change the flow path area of the exhaust gas flow path, an actuator (motor actuator) which displaces (rotates) the nozzle vanes, and the like. By changing the opening degree of the nozzle vanes to change the flow path area (throat area) between adjacent nozzle vanes, the flow rate of exhaust gas introduced toward the turbine wheel is adjusted (see, for example, PTL 1 and 2). Thus, by adjusting the exhaust gas flow rate, the rotational speeds of the turbine wheel and the compressor impeller can be adjusted to regulate the pressure of air introduced into the combustion chamber of the engine.
The increased flexibility of adjustment of the boost pressure caused by the energy of exhaust gas imparts, to the variable nozzle vane turbocharger, advantages such as an improvement in torque response which will contribute to acceleration, an improvement in the flexibility of adaptation to power, fuel efficiency (fuel consumption), emissions, and the like. Note that there is a growing use of the variable nozzle vane turbocharger for gasoline engines in addition to diesel engines.
[Citation List]
[Patent Literature]
    [PTL 1] JP 2009-299505 A    [PTL 2] JP 2003-129853 A    [PTL 3] JP 2009-281144 A